IRON AND IRON-NICKEL SULFIDES IN CHONDRITIC INTERPLANETARY DUST PARTICLES

We report the results of a study of iron and iron-nickel sulfides in chondritic anhydrous and hydrated interplanetary dust particles (IDPs). The IDPs were characterized using chemical and mineralogical techniques including energy dispersive X-ray analyses and transmission electron microscopy. It is widely believed that the first sulfur-containing mineral to form in the early solar nebula should have been stoichiometric FeS (troilite), and that pyrrhotite is of secondary origin. All examined interplanetary dust particles, both anhydrous and hydrous types, contain more pyrrhotite than troilite, suggesting that the former was a common, possibly predominant nebular condensate phase. Pyrrhotite could form from sulfidation of troilite, after the latter had exfoliated from substrate metal grains. In contrast to anhydrous IDPs, hydrated ones contain Ni-rich sulfides, including pentlandite, which are probably of secondary origin.